The present invention relates to an apparatus and method for debarking logs prior to further processing such as lumber production or production of wood chips.
Log debarking is typically accomplished using ring debarkers or drum debarkers. In a ring debarker, a log passes through a ring of abrasive or cutting heads which contact the circumference of the log. By necessity, a ring debarker may only handle one log at a time and therefore multiple units operating at high speeds are required for efficient processing of small diameter stems. As well, ring debarkers are subject to high stresses from the impact of logs propelled at high speed from the log delivery system.
A drum debarker has a continuously rotating drum which is partially filled with logs (usually from 30 to 40% full by volume) and as the drum rotates, the log burden inside the drum is lifted causing the logs to cascade down and roll back on and impact the logs below. It is this continuously lifting, rotational and impacting/rubbing action of logs on each other that removes the bark as the logs progress down the drum toward the discharge gate. The logs are usually fed into the drum in a continuous stream of groups of logs from an elevated hopper at one end of the drum and slide by gravity into the drum. Although drum debarkers can process large volumes of logs, pretreatment is usually required to achieve acceptable debarking cleanliness when dealing with severe winter conditions (frozen logs) or difficult to debark species.
Rotary debarkers exist which use rollers having debarking teeth or bars. An example of a rotary debarker is the Fuji King debarker designed by Fuji Kogyo and licensed to CAE in Canada. In this example, the debarker consists of a fixed trough assembly containing a pair of openings to allow the placement of a cylindrical rotor in each opening. The rotors are mounted at their ends on roller bearings and are driven with electrical drives. Mounted on the surfaces of the rotors are debarking plates. The rotors are very tight within their openings and the protruding plates pass through slits in the edges of these openings. Logs and branches typically are fed into the debarker with a transverse chain deck. The deck feeds an infeed hopper that delivers the logs into the trough in the same axis as the rotors. As the furnish enters the debarker, it is impacted by the plates on the surface of the spinning rotors. The contact of these plates begins the removal of bark by first breaking the bond with the fiber at the cambium layer. Additionally, the plates cause the logs to spin about their own axis and move within the trough, contacting the other logs and branches. Bark is abraded from the logs through mutual contact and the striking of the plates.
The wood fibre debris processor disclosed in co-owned U.S. Pat. No. 5,394,912 (the contents of which are hereby incorporated in its entirety) may also be used as an effective debarker machine. Like the Fuji King debarker, the logs are fed into one end of the apparatus and discharged at the other end, traveling in a direction consistent with their longitudinal axis.
However, there is a need in the art for rotary type debarker which mitigates the disadvantages of the prior art and which improves upon or provides an effective alternative to the prior art.